Blue phosphor, light-emitting device, and plasma display panel

ABSTRACT

The present invention provides a blue phosphor that exhibits high luminance and shows less luminance degradation during driving of a light-emitting device. The present invention is a blue phosphor represented by the general formula aBaO.bSrO.(1−a−b)EuO.cMgO.dAlO 3/2 .eWO 3 , where 0.70≦a≦0.95, 0≦b≦0.15, 0.95≦c≦1.15, 9.00≦d≦11.00, 0.001≦e≦0.100, and a+b≦0.97 are satisfied. In this blue phosphor, two peaks whose tops are located in a range of diffraction angle 2θ=13.0 to 13.6 degrees are present in an X-ray diffraction pattern obtained by measurement on the blue phosphor using an X-ray with a wavelength of 0.774 Å.

TECHNICAL FIELD

The present invention relates to a blue phosphor that is used in aplasma display panel (PDP), a mercury-free fluorescent lamp, or thelike, and to a light-emitting device (particularly a PDP).

BACKGROUND ART

Various aluminate phosphors have been put to practical use as phosphorsfor energy-saving fluorescent lamps. Examples of blue phosphors include(Ba,Sr)MgAl₁₀O₁₇:Eu (BAM:Eu), and examples of green phosphors includeCeMgAl₁₁O₁₉:Tb and BaMgAl₁₀O₁₇:Eu,Mn.

In recent years, BAM:Eu, which exhibits high luminance undervacuum-ultraviolet excitation, has been used as a blue phosphor forPDPs.

However, when a light-emitting device using the blue phosphor BAM:Eu isdriven for a long period of time, the luminance is degradedsignificantly. Hence, for use in a light-emitting device, particularlyin a PDP, there is a strong demand for a phosphor that shows lessluminance degradation even after long-time driving.

The mechanism of luminance degradation of the blue phosphor BAM:Eu hasnot been clarified sufficiently. The luminance degradation of the bluephosphor is likely to occur because of the entry of moisture andimpurity gas as well as the heat treatment in the process ofmanufacturing the light-emitting device, and of the vacuum ultravioletlight irradiation during driving of the light-emitting device.

In order to prevent the luminance degradation, there have been proposeda method in which gadolinium is added to a phosphor (see JP6(1994)-29418 B, for example), a method in which a phosphor is coatedwith silicate of divalent metal such as alkaline earth metal (see JP2000-34478 A, for example), and a method in which a phosphor is coatedwith an antimony oxide (see JP 10(1998)-330746 A, for example).

However, light-emitting devices using the phosphors according to theseconventional methods, in most cases, cannot suppress the luminancedegradation of the phosphor during driving while maintaining highluminance.

DISCLOSURE OF THE INVENTION

The present invention has been made in order to solve theabove-mentioned conventional problems, and it is an object of thepresent invention to provide a blue phosphor that exhibits highluminance and shows less luminance degradation during driving of alight-emitting device. It is a further object of the present inventionto provide a long-life light-emitting device, particularly a PDP, usingthe blue phosphor.

The present invention is a blue phosphor represented by the generalformula aBaO.bSrO.(1−a−b)EuO.cMgO.dAlO_(3/2).eWO₃, where 0.70≦a≦0.95,0≦b≦0.15, 0.95≦c≦1.15, 9.00≦d≦11.00, 0.001≦e≦0.100, and a+b≦0.97 aresatisfied. In this blue phosphor, two peaks whose tops are located in arange of diffraction angle 2θ=13.0 to 13.6 degrees are present in anX-ray diffraction pattern obtained by measurement on the blue phosphorusing an X-ray with a wavelength of 0.774 Å. In this blue phosphor, itis preferable that 0.80≦a≦0.95, 0≦b≦0.05, 1.00≦c≦1.15, 9.50≦d≦10.00, and0.005≦e≦0.020 are satisfied. It also is preferable that one of the twopeaks has its top in a range of diffraction angle 2θ=13.0 to 13.2degrees in the X-ray diffraction pattern obtained by measurement on theblue phosphor using an X-ray with a wavelength of 0.774 Å.

In another aspect, the present invention is a light-emitting deviceincluding a phosphor layer containing the blue phosphor, and a suitableexample of the light-emitting device is a plasma display panel.

The plasma display panel includes, for example: a front panel; a backpanel that is arranged to face the front panel; barrier ribs that definea clearance between the front panel and the back panel; a pair ofelectrodes that are disposed on the back panel or the front panel; anexternal circuit that is connected to the electrodes; a discharge gasthat is present at least between the electrodes and contains xenon thatgenerates a vacuum ultraviolet ray by applying a voltage between theelectrodes through the external circuit; and phosphor layers that emitvisible light induced by the vacuum ultraviolet ray, the phosphor layersinclude a blue phosphor layer, and the blue phosphor layer contains theblue phosphor.

The present invention can provide a blue phosphor that exhibits highluminance and shows less luminance degradation during manufacturing anddriving of the light-emitting device. The present invention also canprovide a long-life light-emitting device, such as a PDP, in which theluminance is not degraded even after long-time driving.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a structure of a PDPof the present invention.

FIG. 2 shows a powder X-ray diffraction pattern of Sample No. 5 measuredas Example.

FIG. 3 shows a powder X-ray diffraction pattern of Sample No. 13measured as Example.

FIG. 4 shows a powder X-ray diffraction pattern of Sample No. 2 measuredas Comparative Example.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail.

<Composition of Blue Phosphor>

The blue phosphor of the present invention is represented by the generalformula aBaO.bSrO.(1−a−b)EuO.cMgO.dAlO_(3/2).eWO₃, where 0.70≦a≦0.95,0≦b≦0.15, 0.95≦c≦51.15, 9.00≦d≦11.00, 0.001≦e≦0.100, and a+b≦0.97 aresatisfied. With respect to coefficients a, b, c, d and e, preferableranges are 0.80≦a≦0.95, 0≦b≦0.05, 1.00≦c≦1.15, 9.50≦d≦10.00, and0.005≦e≦0.020, respectively, from the viewpoints of luminance andresistance to luminance degradation.

<Characteristics Relating to X-Ray Diffraction of Blue Phosphor>

The blue phosphor of the present invention is characterized in that twopeaks whose tops are located in a range of diffraction angle 2θ=13.0 to13.6 degrees are present in an X-ray diffraction pattern obtained bymeasurement on the blue phosphor using an X-ray with a wavelength of0.774 Å. From the viewpoints of luminance and resistance to luminancedegradation, it is preferable that one of the two peaks has its top in arange of diffraction angle 2θ=13.0 to 13.2 degrees in the X-raydiffraction pattern obtained by measurement on the blue phosphor usingan X-ray with a wavelength of 0.774 Å.

The present inventors have found from their extensive experimentalstudies that a blue phosphor having the above composition and having theabove characteristics relating to the X-ray diffraction pattern can be aphosphor that exhibits high luminance and shows less luminancedegradation during manufacturing and driving of a light-emitting device.With respect to the conventional blue phosphor BAM:Eu, the number ofpeaks whose tops are located in the above range of diffraction angle 2θis only one. The reason why the blue phosphor having the abovecharacteristics relating to the X-ray diffraction pattern has excellentlight-emitting property is not clear, but it is presumed as follows. Inthe experiments conducted by the present inventors, a phosphor wassubjected to firing under unique conditions as described later. It isconsidered that the lattice constant of the phosphor changes during thisfiring, which results in an improvement in the light-emitting property(resistance to luminance degradation) of the phosphor.

In the present invention, in order to distinguish a peak from a changein signal intensity due to noise and the like in the X-ray diffractionpattern, among the changes in signal intensity, a change in signalintensity having an intensity of at least one tenth of a peak present inthe vicinity of a diffraction angle 2θ=13.4 degrees is recognized as apeak. In the present invention, the phrase “two peaks are present”refers to the case where the sign of the differential value at eachangle point constituting the spectrum is reversed three times within apredetermined range of diffraction angle, while ignoring noise.Therefore, here, even in the case where two peaks overlap so as toconstitute one bimodal peak, it is considered as “two peaks arepresent”.

<Powder X-Ray Diffraction Measurement>

Next, a powder X-ray diffraction measurement on the blue phosphor of thepresent invention will be described.

For the powder X-ray diffraction measurement, for example, BL19B2 powderX-ray diffraction equipment (Debye-Scherrer optical system using animaging plate; hereinafter referred to as BL19 diffraction equipment) inthe large-scale synchrotron radiation facility, SPring 8 is used.Phosphor powder is packed tightly into a Lindemann glass capillary withan internal diameter of 200 μm. The incident X-ray wavelength is set toapproximately 0.774 Å using a monochromator. While a sample is rotatedwith a goniometer, the diffraction intensity is recorded on the imagingplate. The measuring time is to be determined, paying attention to keepthe imaging plate unsaturated. The measuring time is, for example, 5minutes. The imaging plate is developed and an X-ray diffractionspectrum thereon is read out.

It should be noted that an error from the zero point when the data isread out from the developed imaging plate is approximately 0.03 in termsof diffraction angle 2θ.

An accurate incident X-ray wavelength is confirmed using a CeO₂ powder(SRM No. 674a) of NIST (National Institute of Standards and Technology)whose lattice constant is 5.4111 Å. The data measured on the CeO₂ powderis subjected to Rietveld analysis while varying only the latticeconstant (a-axis length). The actual X-ray wavelength λ is calculatedbased on the difference between the value a′ obtained for thepredetermined X-ray wavelength λ′ and the actual value (a=5.4111 Å) fromthe following formula.λ=aλ′/a′

For the Rietveld analysis, RIETAN-2000 program (Rev. 2.3.9 or later;hereinafter referred to as RIETAN) is used (see NAKAI Izumi, IZUMIFujio, “Funmatsu X-sen kaiseki-no-jissai—Rietveld hou nyumon” (Practiceof powder X-ray analysis—introduction to Rietveld method), DiscussionGroup of X-Ray Analysis, the Japan Society for Analytical Chemistry,Asakura Publishing, 2002, and http://homepage.mac.com/fujioizumi/).

It should be noted that X-ray diffraction is a phenomenon that isobserved when a crystal lattice, incidence of X-ray, and a geometry ofdiffraction satisfy the Bragg's condition:2d sin θ=nλThough the spectrum can be observed using a commonly available X-raydiffractometer, the diffraction profile observed has some differencesbecause the observed strength depends on the incident X-ray wavelength.

<Manufacturing Method of Phosphor>

Hereinafter, the method of manufacturing the phosphor of the presentinvention will be described. The method of manufacturing the phosphor ofthe present invention is not limited to the method described below.

As a barium source material, a barium compound that can be convertedinto barium oxide by firing, such as barium hydroxide, barium carbonate,barium nitrate, barium halide, and barium oxalate, each having highpurity (purity of 99% or more), may be used. Barium oxide having highpurity (purity of 99% or more) also may be used.

As a strontium source material, a strontium compound that can beconverted into strontium oxide by firing, such as strontium hydroxide,strontium carbonate, strontium nitrate, strontium halide, and strontiumoxalate, each having high purity (purity of 99% or more), may be used.Strontium oxide having high purity (purity of 99% or more) also may beused.

As a europium source material, a europium compound that can be convertedinto europium oxide by firing, such as europium hydroxide, europiumcarbonate, europium nitrate, europium halide, and europium oxalate, eachhaving high purity (purity of 99% or more), may be used. Europium oxidehaving high purity (purity of 99% or more) also may be used.

As a magnesium source material, a magnesium compound that can beconverted into magnesium oxide by firing, such as magnesium hydroxide,magnesium carbonate, magnesium nitrate, magnesium halide, magnesiumoxalate, and basic magnesium carbonate, each having high purity (purityof 99% or more), may be used. Magnesium oxide having high purity (purityof 99% or more) also may be used.

As an aluminum source material, an aluminum compound that is convertedinto alumina by firing, such as aluminum hydroxide, aluminum nitrate,and aluminum halide, each having high purity (purity of 99% or more),may be used. Alumina having high purity (purity of 99.9% or more) alsomay be used.

As a tungsten source material, various source materials that can beconverted into oxides may be used in the same way.

The blue phosphor is manufactured by mixing the above source materialsand firing the mixed powder. The method of mixing the source materialsmay be wet mixing in a solution or dry mixing of dry powders. A ballmill, a stirred media mill, a planetary mill, a vibration mill, a jetmill, a V-type mixer, an agitator, and the like, which are in generalindustrial use, may be used. Since coarse particles in the sourcematerials adversely affect the light-emitting property, it is preferablethat the particles are classified to improve particle size uniformity.

Firing of the mixed powder is carried out, for example, in a mixed gascontaining hydrogen, nitrogen and oxygen at 900 to 1600° C. for 1 to 50hours. In the mixed gas, the concentration of hydrogen may be 0.1 to 10%by volume and the partial pressure of oxygen may be adjusted toapproximately 10⁻¹² to 10⁻⁷. By firing the mixed powder under theseunique conditions, a blue phosphor having the above-mentionedcharacteristics relating to the X-ray diffraction pattern can beobtained efficiently.

As a furnace to be used for the firing, furnaces that are in generalindustrial use may be used. A gas furnace or an electric furnace of thebatch type or continuous type such as a pusher furnace may be used.

When a hydroxide, a carbonate, a nitrate, a halide, an oxalate or thelike that can be converted into oxide by firing is used as a sourcematerial, it is preferable that pre-firing is carried out within atemperature range of 800 to 1500° C. before main firing. A flux, such asmaterial fluoride, preferably is added in order to accelerate thereaction.

The particle size distribution and flowability of the phosphor powdercan be adjusted by crushing the obtained phosphor powder again using aball mill, a jet mill, or the like, and further by washing orclassifying it, if necessary.

<Uses of Blue Phosphor>

A light-emitting device exhibiting high luminance and resistance toluminance degradation can be constructed by applying the blue phosphorof the present invention to a light-emitting device having a phosphorlayer. Specifically, for a light-emitting device having a phosphor layerin which BAM:Eu is used, BAM:Eu is replaced with the blue phosphor ofthe present invention, while a light-emitting device may be constructedaccording to a known method. It also is possible to construct alight-emitting device in which the phosphor of the present invention anda light-emitting diode (LED) chip are used in combination. Examples ofthe light-emitting device include a PDP, a fluorescent panel, and afluorescent lamp, and among them, a PDP is suitable.

Hereinafter, an embodiment (the PDP of the present invention) in whichthe blue phosphor of the present invention is applied to a PDP will bedescribed with an example of an AC surface-discharge type PDP. FIG. 1 isa cross-sectional perspective view showing the basic structure of an ACsurface-discharge type PDP 10. It should be noted that the PDP shownhere is illustrated for convenience with a size that is appropriate fora specification of 1024×768 pixels, which is the 42-inch class, and thepresent invention may be applied to other sizes and specifications aswell.

As illustrated in FIG. 1, this PDP 10 includes a front panel 20 and aback panel 26, and these panels are arranged with their main surfacesfacing each other.

The front panel 20 includes a front panel glass 21 as a front substrate,strip-shaped display electrodes (X-electrode 23, Y-electrode 22)provided on one main surface of the front panel glass 21, a front-sidedielectric layer 24 having a thickness of approximately 30 μm coveringthe display electrodes, and a protective layer 25 having a thickness ofapproximately 1.0 μm provided on the front-side dielectric layer 24.

The above display electrode includes a strip-shaped transparentelectrode 220 (230) having a thickness of 0.1 μm and a width of 150 μm,and a bus line 221 (231) having a thickness of 7 μm and a width of 95 μmand laid on the transparent electrode. A plurality of pairs of thedisplay electrodes are disposed in the y-axis direction, where thex-axis direction is a longitudinal direction.

The display electrodes (X-electrode 23, Y-electrode 22) of each pair areconnected electrically to a panel drive circuit (not shown) respectivelyin the vicinity of the ends of the width direction (y-axis direction) ofthe front panel glass 21. It should be noted that the Y-electrodes 22are connected collectively to the panel drive circuit and theX-electrodes 23 each are connected independently to the panel drivecircuit. When the Y-electrodes 22 and the certain X-electrodes 23 arefed using the panel drive circuit, a surface discharge (sustaineddischarge) is generated in the gap (approximately 80μ) between theX-electrode 23 and the Y-electrode 22. The X-electrode 23 also canoperate as a scan electrode, and in this case, a write discharge(address discharge) can be generated between the X-electrode 23 and anaddress electrode 28 to be described later.

The above-mentioned back panel 26 includes a back panel glass 27 as aback substrate, a plurality of address electrodes 28, a back-sidedielectric layer 29, barrier ribs 30, and phosphor layers 31 to 33, eachof which corresponds to one color of red (R), green (G), and blue (B).The phosphor layers 31 to 33 are provided so that they contact with theside walls of two adjacent barrier ribs 30 and with the back-sidedielectric layer 29 between the adjacent barrier ribs 30, and repeatedlyare disposed in sequence in the x-axis direction.

The blue phosphor layer (B) contains the above-mentioned blue phosphorof the present invention. On the other hand, the red phosphor layer andthe green phosphor layer contain commonly-used phosphors. Examples ofthe red phosphor include (Y,Gd)BO₃:Eu and Y₂O₃:Eu, and examples of thegreen phosphor include Zn₂SiO₄:Mn, YBO₃:Tb, and (Y,Gd)BO₃:Tb.

Each phosphor layer can be formed by applying a phosphor ink in whichphosphor particles are dissolved to the barrier ribs 30 and theback-side dielectric layer 29 by a known applying method such as ameniscus method and a line jet method, and drying and firing them (e.g.,at 500° C., for 10 minutes). The above-mentioned phosphor ink can beprepared, for example, by mixing 30% by mass of a blue phosphor having avolume average particle diameter of 2 μm, 4.5% by mass of ethylcellulose with a weight average molecular weight of approximately200,000, and 65.5% by mass of butyl carbitol acetate. In this regard, itis preferable that the viscosity thereof is adjusted eventually toapproximately 2000 to 6000 cps (2 to 6 Pas), because the adherence ofthe ink to the barrier ribs 30 can be enhanced.

The address electrodes 28 are provided on the one main surface of theback panel glass 27. The back-side dielectric layer 29 is provided so asto cover the address electrodes 28. The barrier ribs 30 have a height ofapproximately 150 μm and a width of approximately 40 μm, and thelongitudinal direction is in the y-axis direction. The barrier ribs 30are provided on the back-side dielectric layer 29 so as to correspond tothe pitch of the adjacent address electrodes 28.

Each of the address electrodes 28 has a thickness of 5 μm and a width of60 μm. A plurality of address electrodes 28 are disposed in the x-axisdirection, where the y-axis direction is a longitudinal direction. Theaddress electrodes 28 are disposed at a certain pitch (approximately 150μm). A plurality of address electrodes 28 each are connectedindependently to the above-mentioned panel drive circuit. Addressdischarge can be generated between a certain address electrode 28 and acertain X-electrode 23 by feeding each address electrode individually.

The front panel 20 and the back panel 26 are disposed so that theaddress electrode 28 and the display electrode are orthogonal to eachother. The peripheral portions of both the panels 20 and 26 are bondedand sealed with a frit glass sealing portion (not shown) that serves asa sealing member.

An enclosed space between the front panel 20 and the back panel 26,which has been bonded and sealed with the frit glass sealing portion, isfilled with a discharge gas composed of a rare gas such as He, Xe and Neat a predetermined pressure (ordinarily approximately 6.7×10⁴ to 1.0×10⁵Pa).

It should be noted that a space corresponding to a space between twoadjacent barrier ribs 30 is a discharge space 34. A region where a pairof display electrodes intersect with one address electrode 28 with thedischarge space 34 disposed therebetween corresponds to a cell used fordisplaying an image. It should be noted that in this embodiment, thecell pitch in the x-axis direction is set to approximately 300 μm andthe cell pitch in the y-axis direction is set to approximately 675 μm.

When the PDP 10 is driven, an address discharge is generated by applyinga pulse voltage to the certain address electrode 28 and the certainX-electrode 23 by the panel drive circuit, and after that, a sustaineddischarge is generated by applying a pulse between a pair of displayelectrodes (X-electrode 23, Y-electrode 22). The phosphors contained inthe phosphor layers 31 to 33 are allowed to emit visible light using theultraviolet ray with a short wavelength (a resonance line with a centralwavelength of approximately 147 nm and a molecular beam with a centralwavelength of 172 nm) thus generated. Thereby, a prescribed image can bedisplayed on the front panel side.

The blue phosphor of the present invention can be applied to afluorescent panel including a fluorescent layer that is excited by anultraviolet ray and then emits light according to a known manner. Thisfluorescent panel has good luminance as well as an excellent resistanceto luminance degradation compared to the conventional fluorescentpanels. This fluorescent panel can be used, for example, as a backlightof a liquid crystal display device.

The blue phosphor of the present invention can be applied also to afluorescent lamp (e.g., electrodeless fluorescent lamp, xenonfluorescent lamp, fluorescent mercury lamp) according to a known manner.This fluorescent lamp has good luminance as well as an excellentresistance to luminance degradation compared to the conventionalfluorescent lamps.

Hereinafter, an embodiment of the present invention will be described inmore detail with reference to Examples. The present invention is notlimited by these Examples.

<Preparation of Phosphor Samples of Examples>

As starting materials, BaCO₃, SrCO₃, MgCO₃, Al₂O₃, AlF₃, Eu₂O₃, and WO₃were used. These materials were weighed according to the compositionsshown in Table 1, and wet-mixed in pure water using a ball mill. Afterthese mixtures were dried, they were pre-fired in an air atmosphere at1200 to 1500° C. for 4 hours. The obtained fired mixtures were subjectedto main firing at 1200 to 1500° C. for 4 hours, and thus phosphors(Sample Nos. 4 to 14) were obtained. It should be noted that the mainfiring was carried out by employing a unique firing method, in which thefiring was carried out under a mixed gas atmosphere containing hydrogen,nitrogen and oxygen (in which the concentration of hydrogen was 3% byvolume, and the partial pressure of oxygen was approximately 10⁻¹² to10⁻⁷ at a peak temperature), and in the process of temperature dropping,introduction of hydrogen was stopped at a temperature of 800 to 1000° C.

<Preparation of Phosphor Samples of Comparative Examples>

Phosphors of Sample Nos. 1 to 3, 15 and 16 were prepared in the samemanner as in the above-mentioned phosphor samples of Examples, exceptthat the main firing was carried out in a typical reducing atmosphereusing nitrogen containing 3% by volume of hydrogen (in which the partialpressure of oxygen was approximately 10⁻¹⁵ at a peak temperature)without using WO₃. A phosphor of Sample No. 17 was prepared in the samemanner as in the above-mentioned phosphor samples of Examples, exceptthat the main firing was carried out in a typical reducing atmosphereusing nitrogen containing 3% by volume of hydrogen (in which the partialpressure of oxygen was approximately 10⁻¹⁵ at a peak temperature).

<Powder X-Ray Diffraction Measurement>

The X-ray diffraction patterns of the phosphor samples of Examples andComparative Examples were measured by the above-mentioned method, usingBL19 diffraction equipment in the large-scale synchrotron radiationfacility, SPring 8. Table 1 shows, for each of the phosphor samples, thenumber of peaks whose tops are located in the range of diffraction angle2θ=13.0 to 13.6 degrees in the obtained X-ray diffraction pattern andthe position(s) of the peak(s), as well as the composition of thesample. The samples marked with an asterisk in Table 1 are the phosphorsof Comparative Examples. FIGS. 2 to 4 show examples of the obtainedX-ray diffraction patterns (of Samples Nos. 2, 5 and 13).

<Measurement of Luminance>

The measurement of luminance was carried out by irradiating thephosphors with a vacuum ultraviolet ray with a wavelength of 146 nmunder vacuum and measuring light-emission in the visible region. Theluminance is luminance Y in the XYZ color coordinate system ofInternational Commission on Illumination and was evaluated as a valuerelative to the standard sample BAM:Eu (Ba_(0.9)MgAl₁₀O₁₇:Eu_(0.1)).Table 1 shows the results.

TABLE 1 Sam- Peak ple Number position Y No. a b c d e of peaks (degrees)(%) *1 0.65 0.25 0.90 8.00 0 1 13.40 70 *2 0.70 0.20 1.00 10.00 0 113.38 85 *3 0.97 0 1.20 12.00 0 1 13.34 75  4 0.70 0.15 0.95 9.00 0.0012 13.30, 13.42 100  5 0.90 0.05 1.15 10.00 0.100 2 13.25, 13.40 102  60.90 0.05 1.15 11.00 0.010 2 13.28, 13.42 105  7 0.85 0.05 1.00 9.500.005 2 13.30, 13.40 115  8 0.80 0.05 1.15 10.00 0.020 2 13.28, 13.40112  9 0.90 0 1.00 10.00 0.010 2 13.18, 13.38 120 10 0.90 0.02 1.15 9.700.010 2 13.18, 13.40 118 11 0.80 0.05 1.00 9.50 0.005 2 13.18, 13.42 11712 0.95 0 1.00 10.00 0.020 2 13.16, 13.36 116 13 0.91 0 1.00 10.00 0.0102 13.16, 13.38 125 14 0.90 0 1.00 9.80 0.005 2 13.18, 13.38 122 *15 0.80 0.10 1.00 12.00 0 1 13.40 88 *16  0.80 0.10 1.00 10.00 0 1 13.40 92*17  0.70 0.15 0.95 9.00 0.001 1 13.44 90

As is clear from Table 1, phosphors, each having a composition fallingwithin the composition range of the present invention and having twopeaks whose tops are located in the range of diffraction angle 2θ=13.0to 13.6 degrees, exhibit high luminance under vacuum-ultravioletexcitation. Particularly, phosphors (Sample Nos. 7 to 14) that satisfy0.80≦a≦0.95, 0≦b≦0.05, 1.00≦c≦1.15, 9.50≦d≦10.00, and 0.005≦e≦0.020exhibit high luminance. Furthermore, phosphors (Sample Nos. 9 to 14),each having two peaks, one of which has its top in the range ofdiffraction angle 2θ=13.0 to 13.2 degrees, exhibit particularly highluminance.

<Panel Luminance and Luminance Degradation>

PDPs having the structure of FIG. 1 were manufactured according to theabove-described embodiment of an AC surface-discharge type PDP, usingthe blue phosphors obtained in the same manner as in the phosphors ofSamples Nos. 1 to 17. The initial luminance of each of the PDPs thusmanufactured (as relative values with respect to that of the standardsample BAM:Eu) was measured. Each panel was subjected to accelerateddriving (equivalent to 1000 hours of actual driving), and the luminanceafter the driving was measured to calculate luminance degradation (%).Each panel displayed a fixed image with one color of blue. Table 2 showsthe results. The samples marked with an asterisk in Table 2 are thephosphors of Comparative Examples.

TABLE 2 Peak Luminance Sample Number position Luminance degradation No.a b c d e of peaks (degrees) (%) (%) *18  0.65 0.25 0.90 8.00 0 1 13.4062 18 *19  0.70 0.20 1.00 10.00 0 1 13.38 80 21 *20  0.97 0 1.20 12.00 01 13.34 71 16 21 0.70 0.15 0.95 9.00 0.001 2 13.30, 13.42 98 9 22 0.900.05 1.15 10.00 0.100 2 13.25, 13.40 100 7 23 0.90 0.05 1.15 11.00 0.0102 13.28, 13.42 108 5 24 0.85 0.05 1.00 9.50 0.005 2 13.30, 13.40 111 425 0.80 0.05 1.15 10.00 0.020 2 13.28, 13.40 112 2 26 0.90 0 1.00 10.000.010 2 13.18, 13.38 117 4 27 0.90 0.02 1.15 9.70 0.010 2 13.18, 13.40118 2 28 0.80 0.05 1.00 9.50 0.005 2 13.18, 13.42 121 3 29 0.95 0 1.0010.00 0.020 2 13.16, 13.36 112 5 30 0.91 0 1.00 10.00 0.010 2 13.16,13.38 122 1 31 0.90 0 1.00 9.80 0.005 2 13.18, 13.38 117 2 *32  0.800.10 1.00 12.00 0 1 13.40 80 14 *33  0.80 0.10 1.00 10.00 0 1 13.40 9015 *34  0.70 0.15 0.95 9.00 0.001 1 13.44 85 14

As is clear from Table 2, it is confirmed that when phosphors, eachhaving a composition falling within the composition range of the presentinvention and having two peaks whose tops are located in the range ofdiffraction angle 2θ=13.0 to 13.6 degrees, are used, the values of thepanel initial luminance are high and luminance degradation is inhibitedsignificantly. Particularly, when phosphors (Sample Nos. 24 to 31) thatsatisfy 0.80≦a≦0.95, 0≦b≦0.05, 1.00≦c≦1.15, 9.50≦d≦10.00, and0.005≦e≦0.020 are used, excellent luminance and resistance to luminancedegradation are obtained. Furthermore, when phosphors (Samples 26 to31), each having two peaks, one of which has its top in the range ofdiffraction angle 2θ=13.0 to 13.2 degrees, are used, particularlyexcellent luminance and resistance to luminance degradation areobtained. In contrast, when the samples of Comparative Examples, each inwhich at least one of the coefficients a, b, c, d and e or the number ofspecific peaks in the powder X-ray diffraction measurement is outsidethe respective ranges specified in the present invention, are used, thevalues of the initial luminance are low and the luminance is degradedsignificantly during driving of the PDP.

INDUSTRIAL APPLICABILITY

The blue phosphor of the present invention can be used in light-emittingdevices, among them in particular, PDPs. Furthermore, the blue phosphorof the present invention also can be applied to the uses of fluorescentlamps such as an electrodeless fluorescent lamp, a xenon fluorescentlamp, and a fluorescent mercury lamp, fluorescent panels mainly used fora backlight of a liquid crystal display device, and the like.

1. A blue phosphor represented by the general formulaaBaO.bSrO.(1−a−b)EuO.cMgO.dAlO_(3/2).eWO3, where 0.70≦a≦0.95, 0≦b≦0.15,0.95≦c≦1.15, 5 9.00≦d≦11.00, 0.001≦e≦0.100, and a+b≦0.97 are satisfied,wherein two peaks whose tops are located in a range of diffraction angle2θ=13.0 to 13.6 degrees are present in an X-ray diffraction patternobtained by measurement on the blue phosphor using an X-ray with awavelength of 0.774 Å.
 2. The blue phosphor according to claim 1,wherein 0.80≦a≦0.95, 0≦b≦0.05, 1.00≦c≦1.15, 9.50≦d≦10.00, and0.005≦e≦0.020 are satisfied.
 3. The blue phosphor according to claim 1,wherein one of the two peaks has its top in a range of diffraction angle2θ=13.0 to 13.2 degrees in the X-ray diffraction pattern obtained bymeasurement on the blue phosphor using an X-ray with a wavelength of0.774 Å.
 4. A light-emitting device comprising a phosphor layercontaining the blue phosphor according to claim
 1. 5. The light-emittingdevice according to claim 4, which is a plasma display panel.
 6. Thelight-emitting device according to claim 5, wherein the plasma displaypanel comprises: a front panel; a back panel that is arranged to facethe front panel; barrier ribs that define a clearance between the frontpanel and the back panel; a pair of electrodes that are disposed on theback panel or the front panel; an external circuit that is connected tothe electrodes; a discharge gas that is present at least between theelectrodes and contains xenon that generates a vacuum ultraviolet ray byapplying a voltage between the electrodes through the external circuit;and phosphor layers that emit visible light induced by the vacuumultraviolet ray, phosphor layers include a blue phosphor layer, and theblue phosphor layer contains the blue phosphor.
 7. The blue phosphoraccording to claim 1, wherein the blue phosphor is formed by firing amixture of raw materials at a temperature in a range of 900 to 1600° C.for 1 to 50 hours in an atmosphere containing nitrogen gas, hydrogen gasin an amount of 0.1 to 10% by volume, and oxygen gas in an amount of10⁻¹² to 10⁻⁷ as partial pressure.